Bushing for transformer casings



Jan. 28, 1936. D, TREANOR BUSHING FOR TRANSFORMER CASINGS Filed Nov. 1,1934 m w =2 3mm N Ut e w vd WW d Ey b Patented Jan. 28, 1936 PATENTOFFICE BUSHING FOR TRANSFORMER CASINGS Edward D. Treanor, Pittsfield,Mass, assignor to General Electric Company, a corporation of New YorkApplication November 1, 1934,- Serial No. 750,993

3 Claims.

My invention relates to bushings for transformer casings. Metal casingsfor transformers, particularly of the distribution type, are oftenprovided with overhanging pockets in the side walls, the leads from thetransformer windings being brought out of the casings through theinsulating bushings extendingthrough these pockets and with the outerends of the bushings extending downwardly from the pockets and adjacentthe side walls of the casings. The general object of the invention is toprovide an improved construction and arrangement of bushings of thistype which shall be compact and mechanically well protected frombreakage and 5 which will offer eifective protection to the transformerfrom excessive voltages on circuits con nected thereto through thebushings.

the following description taken in connection with the accompanyingdrawing in which Fig. 1 is a side view of a metal-encased transformerwith a bushing arranged in accordance with the invention, part of thetransformer casing broken away to show details; Fig. 2 is an enlargedsectional view of the bushing with a small adjacent section of thetransformer casing; and Fig. 3 is a. view of the outer end of thebushing.

Like reference characters indicate similar parts in the differentfigures of the drawing. The transformer l0 shown in the drawing isimmersed in an insulating liquid H in a metal casing 12 having anoutwardly projecting side pocket 13. An insulating bushing l4, which maybe formed of porcelain, is secured through an opening in the bottom ofthe pocket l3 by a clamp I 5, a gasket l6 being provided to seal thejoint between the edge of the opening in the pocket l3 and a shoulder onthe bushing I4. The upper end of the bushing I4 is curved inwardlythrough the pocket l3 and. into the interior of the casing l2. A lead I!from a winding of the transformer It! extends through the bushing to anoutside terminal l8 sealed through the outer end of the bushing andprovided with a clamp 19 to permit a conductor 20 of an external circuitto be secured to the terminal.

The metal casing l2 may be and usually is at ground potential and theterminal l8, which is often at rather a high potential, must besulficlently spaced from the casing to prevent an are between these twoparts. It is desirable, however, that the outer end of the bushing l4and terminal "3 be as close as possible to the adjacent side wall of thecasing l2 in order to require no unnecessary floor space and also to beThe invention will be better understood from mechanically protected asmuch as possible by the overhanging pocket l3. To secure theseadvantages the outer end of the bushing I4 is provided with an integralflange or wall 2| projecting between the terminal I8 and an adjacentside 5 wall of the casing I2. This flange increases considerably thebreakdown distance between the terminal and the casing and permits theterminal I 8, and therefore the outer end of the bushing, to bepositioned close to the casing and under the 10 pocket l3 so as torequire minimum floor space and secure maximum mechanical protectionfrom the overhanging pocket.

A metal electrode 22 is secured to the terminal [8 and projects awayfrom the casing l2 through 15 an opening 23 in the side of the flange 2iopposite the casing. The outer end of the electrode 22 may be curvedupwardly toward the adjacentouter portion of the pocket [3. The externallead 20 may also pass from the terminal I8 20 through the opening 23 inthe flange 2|.

The outer end of the bushing M with the terminal [8 projects below thelevel of the insulating liquid in the casing I2 andif an arc shouldoccur between the terminal l8 and the adjacent side 25 wall of thecasing I2 a hole might be burned in the casing wall with seriousresults. Considerable liquid would escape and this liquid is usuallyhighly inflammable and especially so when at the operating temperatureof the transformer. 30 The are very probably would ignite the escapingliquid and a serious fire would result. The outer end of. the electrode22 should consequently be spaced suificiently near the outer part of thepocket l3 to provide a preferential breakdown 35 path for any are due toexcessive voltage of the I terminal l8 such as might result fromlightning or other surge reaching the terminal by way of the externalcircuit conductor 20. The outer portion of the pocket I3 is above thelevel of the liquid in the casing l2 so that if a hole is burned in thepocket I3 by an are, no liquid can escape.

It is desirable of course that the voltage necessary to start an arebetween the electrode 22 and the pocket l3 be less than that which mightcause 45 damage to the transformer l0 and its windings so that thetransformer is protected from electrical disturbances in theexternalcircuit to which it is connected.

The invention and its-advantages have been 5i explained by describingand illustrating a preferred form thereof but it will be obvious thatchanges may be made without departing from the spirit of. the inventionand the scope of the appended claims. 55

1. A transformer casing having an overhangingside pocket, an insulatingbushing secured through the bottom of said pocket, a transformerterminal secured in the outer end of said bushing, said bushing havingan integral flange extending between said terminal and the adjacent wallof the casing and having an opening in its side opposite the casing, andan electrode secured to the terminal and extending through said flangeopening with its outer end spaced from the outer part of said pocket toprovide a discharge gap.

' 2. A transformer casing having an overhanging side pocket, aninsulating bushing secured through the bottom of said pocket, atransformer terminal secured in the outer end of said bushing, anelectrode secured to the terminal with its outer end spaced from theouter part of said pocket to provide a discharge gap, and an insu-=lating liquid in said casing with its level between that of saidterminal and said outer part of the pocket.

3. A transformer casing having an overhanging side pocket, an insulatingbushing secured through the bottom of said pocket, a transformerterminal secured in the outer end of said bushing, said bushing havingan integral flange extending between said terminal and the adjacent wallof the casing and having an opening in its side opposite the casing, anelectrode secured to the terminal and extending through said flangeopening with its outer end spaced from the outer part of said pocket toprovide a discharge gap, and an insulating liquid in said casing withits level between that of said terminal and said outer part of thepocket.

EDWARD D; TREANOR.

